Hi Leah,
A lot's been said in this post already, so I figured I'd just stick to the question in the subject line of your post =)
I donated 3 years ago, at age 27, in good health. Right now, I feel great and I'm more active than I was before I had the transplant, oddly enough. I didn't feel at 100% until about a year after surgery, *but* keep in mind everyone heals differently and at a different rate. When I say I didn't feel "100%," I mean I could do pretty much everything as I used to but I kind of felt like I would get tired a little more quickly than before. That's definitely not an issue anymore.
Other quirks, since it seems you're looking at long-term outcomes:
1. Kind of a bummer I have to limit ibuprofen (since it's metabolized in the kidney) and I get fairly regular headaches. Tylenol isn't helpful to me, but my nephrologist said ibuprofen should be ok in limited doses.
2. Did notice alcohol affects me more quickly than it used to, pre-transplant. I've seen no research on this, but heard anecdotally of other donors having the same feeling.
3. I had regular check-ups at my transplant center to follow my kidney function. Now I make sure to have that checked by a regular physician to make sure creatinine and kidney function is on track, and it is.
Good luck with your decision, whatever it may be.